In this thesis, the author designed and implemented GameBuilder, a desktop application targeted towards 11-14 year olds for creating Outdoor AR games. The software attempts to reduce its learning curve by limiting the feature set, using a guided user interface, adding WYSIWIG-like display, and suggesting to the user a model which matches the software model. The author then conducted two studies to test the efficacy of the software. The first study was a free observation of children using the software during a workshop. The second study was a controlled comparative study where two populations designed games using either the GameBuilder or existing software. Based on observations and analysis of designed games, the author concludes that GameBuilder does offer advantages over existing software. Future improvements to the software are suggested.